/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode() {}
 *     ListNode(int val) { this.val = val; }
 *     ListNode(int val, ListNode next) { this.val = val; this.next = next; }
 * }
 */
class code2 {
    // 反转链表（递归）
    public ListNode reverseList(ListNode head) {
        if(head == null || head.next == null) {
            return head;
        }
        ListNode cur = reverseList(head.next);
        //反向连接
        head.next.next = head;
        //原来的断开
        head.next = null;

        return cur;
    }
}